Marine Forecasts

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7 Day Forecast for Marine Location Near Plymouth, MI

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Area Discussion for - Detroit/Pontiac, MI

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FXUS63 KDTX 291925 AFDDTX

Area Forecast Discussion National Weather Service Detroit/Pontiac MI 325 PM EDT Thu Jul 29 2021

DISCUSSION.

NEAR TERM / REST OF TODAY THROUGH TONIGHT

As of 325 PM EDT . Despite humid conditions persisting this afternoon with temperatures topping out in the low/mid 80s with dewpoints stubbornly holding in the upper 60s to around 70, there are signs that relief is on the way as a cold front continues to sag southeast across the region. Northwest surface flow has virtually overtaken all observational sites as of 2 PM, with visible satellite imagery resembling more of a prototypical post-frontal stratocu field characteristic of an increasingly stable low/midlevel atmosphere. Hi- res soundings also depict the increasing midlevel stability in the 700-500 hPa layer noted by increasing column drying thanks in part to broad-scale subsidence settling overhead.

However, there will still be an opportunity for isolated to widely scattered showers and even a stray thunderstorm or two through roughly 8-9 PM mainly east of I-75/US-23 as there remains plentiful SBCAPE/MLCAPE in excess of 1200 J/kg, albeit in an increasingly shortening vertical column to work with. A limited window of upper- level diffluence will also provide weak dynamics to work with as well in addition to potential convergence downwind of Lake Huron in increasingly northerly flow.

Any lingering activity comes to an end after twilight as the trailing 850 hPa front begins to swing through and allows dewpoints to finally fall through the 60s and eventually into the 50s by Friday morning. The result will be low temperatures settling in the mid/upper 50s outside of metro Detroit, with low 60s in the urban heat island. High pressure building across western Lake Superior will further influence the influx of dry air under north/northwest flow, which will allow for a gradual clearing of cloud cover through the night.

SHORT TERM / FRIDAY THROUGH SATURDAY NIGHT

Quiet and pleasant weather for late July standards will prevail across southeast Michigan Friday as the aforementioned high pressure drifts further southeast and briefly settles over the central Great Lakes. The end result will be a dry day with temperatures in the low/mid 70s and comfortable humidity levels as 850 hPa temps fall into the 7-10 C range. Partly cloudy skies can be anticipated, but would not be surprised if cloud cover is more broken than scattered given typical overperformance of boundary layer stratocu in the midsummer. Low temperatures Friday night drop solidly into the 50s region-wide.

The weather pattern turns unsettled again to start the weekend as the surface high pressure moves further southeast towards the Mid- Atlantic and a digging shortwave dives southeast towards the northern Great Lakes amidst broad aggregate troughing over the Northeast CONUS. This dynamic forcing will be the primary focus for scattered thunderstorms during the Saturday afternoon/evening timeframe, with coverage likely greatest north of the I-69 corridor. Southwest flow ahead of the disturbance and associated cold front will allow dewpoints to creep back up into at least the low 60s, yielding MLCAPEs potentially approaching or exceeding 1000 J/kg. Effective shear will also be around 30 knots supporting the potential for a few storms to at least be strong in nature. SPC currently has much of northern Lower in a Marginal Risk for Saturday for mainly a wind threat, and will need to monitor the potential as we get closer. The cold front will then swing through Saturday night into early Sunday morning bringing a more widespread coverage of showers and thunderstorms.

LONG TERM / SUNDAY THROUGH WEDNESDAY

Quasi-split flow sets up for the remainder of Sunday and into early next week as weak high pressure settles over the Great Lakes at the surface, yielding generally stable and dry conditions. Light winds in the low-levels during this time will do little to moderate the thermal and moisture profiles, resulting in temperatures remaining in the 70s to near 80 with dewpoints holding steady in the 50s. The next chance for precipitation may come midweek as long range guidance signals at the split flow breaking down over the Great Lakes as longwave troughing taking hold yet again over the eastern CONUS and embedded pieces of shortwave energy possibly sparking rounds of convection.

MARINE.

A low pressure system moves off to the eastern Great Lakes this afternoon with a pair of cold fronts moving through the central Great Lakes through tonight. Northwest flow around 10 to 15 kt continues early before the secondary front drops across Lake Huron tonight and shifts winds more from the north/northeast with cold advection bringing a gust component of 25+ kt. This with the resultant 4 to 6 ft wave field will lead to hazardous boating conditions across southern Lake Huron, so a Small Craft Advisory has been issued beginning tonight for the nearshore waters around the Thumb. Inner Saginaw Bay may need to be added to the advisory if more of a northeast wind component is able to funnel down the bay. Winds and waves then begin to relax midday Friday as high pressure builds in from the west. The next disturbance clips the region on Saturday with northern Lake Huron standing the best chance to see some showers and storms with it. Another wave leads to continued unsettled conditions into Sunday before a better chance for dry weather arrives during the early part of next week.

HYDROLOGY.

A few lingering showers and isolated thunderstorms will continue through the evening hours mainly across portions of the Thumb and areas east of I-75/US-23 as a cold front continues sagging southeast across the region. Rainfall amounts with this activity will generally remain under a quarter of an inch. Dry weather will then prevail for Friday through Saturday morning. Scattered thunderstorms then return Saturday afternoon into Saturday night associated with an upper-level disturbance traversing the northern Great Lakes. The best chance for thunderstorms at this time looks to reside north of the I-69 corridor. Areawide rainfall totals look to average under a half of an inch, but any thunderstorm will be capable of producing rainfall amounts in excess of 1 inch which may result in poor drainage flooding, especially in susceptible areas that have been especially hard hit over the past few weeks by heavy rainfall.

PREV DISCUSSION. Issued at 1257 PM EDT Thu Jul 29 2021

AVIATION .

Satellite data confirms an ongoing increase in the coverage of diurnally driven strato cu given the ample boundary layer moisture in place. While there is a few lingering MVFR based ceilings, growing boundary layer depth will be more supportive of prevailing VFR conditions. Enhanced convergence along a slow moving cold front currently located between FNT and mbS is triggering a more robust cu field. The front is forecast to begin a more meaningful southward push late this afternoon/evening. By this time, the convective depths will be enough to trigger scattered showers. There is enough support of this potential in latest RAP and NAM to add a couple hours of -SHRA late this afternoon/evening to the TAFs. While the loss of daytime heating will support decrease in the strato cu field this evening, there is enough model support suggesting enough Lake Huron contribution to maintain a good degree of cloud cover in the forecast through the night.

For DTW . The front is not forecast to pass across metro until 23Z. There will however be some veering of the winds toward the northwest ahead of the front, with the actual frontal passage marked by a wind shift to the north.

DTW THRESHOLD PROBABILITIES .

* Moderate in ceilings at or below 5000 feet today and tonight.

DTX WATCHES/WARNINGS/ADVISORIES. MI . Beach Hazards Statement from Friday morning through Friday afternoon for MIZ049-055-063.

Lake Huron . Small Craft Advisory from 10 PM this evening to 4 PM EDT Friday for LHZ421-441>443.

Lake St Clair . NONE. Michigan waters of Lake Erie . NONE.

DISCUSSION . IRL MARINE . TF HYDROLOGY . IRL AVIATION . SC

You can obtain your latest National Weather Service forecasts online at www.weather.gov/detroit.

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Weather Reporting Stations

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Stations	Dist	Age	Wind	Air Temp	Water Temp	Waves	Pressure	DewPt
CLSM4 - St. Clair Shores, MI	33 mi	73 min	N 12 G 14	83°F			1009.1 hPa (-0.4)
THLO1 - Toledo Light No. 2 OH	41 mi	73 min	WNW 11 G 12	81°F
45147 - Lake St Clair	43 mi	73 min	N 5.8 G 7.8	79°F	75°F	1 ft	1008.2 hPa (-0.1)
THRO1 - 9063085 - Toledo, OH	47 mi	55 min	NW 11 G 17				1009 hPa
45165	48 mi	33 min	NNW 9.7 G 12	82°F	79°F	1 ft
TWCO1	48 mi	33 min	WNW 13 G 15		79°F

Wind History for Toledo, OH

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NE4

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NW9 G12

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NW6 G11

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W7 G12

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W7 G11

NW9 G15

W7 G11

W11

NW9 G15

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Airport Reports

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Airport	Dist	Age	Wind kt	Visibility	Sky/Weather	Temp	DewPt	Humidity	Pressure
Detroit, Willow Run Airport, MI	10 mi	20 min	WNW 9	7.00 mi	Fair	89°F	71°F	55%	1009.2 hPa
Detroit, Detroit Metropolitan Wayne County Airport, MI	13 mi	20 min	WNW 8 G 17	10.00 mi	Mostly Cloudy	86°F	70°F	59%	1009.3 hPa
Ann Arbor, Ann Arbor Municipal Airport, MI	17 mi	20 min	NW 9	10.00 mi	Partly Cloudy	84°F	70°F	63%	1009.5 hPa
Troy, Oakland/Troy Airport, MI	20 mi	17 min	NNW 7	10.00 mi	Partly Cloudy	85°F	70°F	60%	1010.5 hPa
Pontiac, Oakland County International Airport, MI	21 mi	20 min	NW 7	10.00 mi	Mostly Cloudy	84°F	68°F	59%	1008.9 hPa

Link to 5 minute data for KYIP

Wind History from YIP (wind in knots)

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N7

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